out of curiosityUsually it's out of curiosity.
natural curiosityForgive an old man's natural curiosity.
insatiable curiosityHis insatiable curiosity and desire for experiment had led to his election as a Fellow of the Royal Society.
curiosity shopIt was like stepping from the main street into a cobbled alley's curiosity shop — that shock of surprise to discover again what an intricate and peculiar organ the imagination is, what extravagant uses it has found for time.
intellectual curiosityhave great intellectual curiosity;
idle curiosityPerhaps it was nothing more than idle curiosity.
curiosity killedPerhaps this is the origin of the old expression ‘curiosity killed the cat’?
scientific curiosityIt is useless for me to point out that scientific curiosity by itself is as irresponsible as the curiosity of a child.